MINNEAPOLIS — Last call had just been announced at the Beverly Hills Hilton’s lobby bar when a PBS executive approached one of the last remaining parties with a question for its most dapper member.

Are you Hugh Bonneville?

Yes, he replied, shaking her hand as she proclaimed her love of his portrayal of stubbornly proud Lord Grantham on “Downton Abbey.”

One problem. Bonneville had retired to his room an hour ago. The practical joker was co-star Brendan Coyle, aka Mr. Bates, the cursed valet. A true gentleman in real life as well, Coyle didn’t reveal his true identity to the star-struck exec.

For her case of mistaken identity, the suit should be sentenced to a two-week stint in Oscar the Grouch’s trash can. “Downton” is a genuine sensation, drawing 5.4 million viewers, on average, for its second season in 2012, a tea-spilling number in the PBS universe. The addicted fanatics among them have been anticipating Sunday’s third-season premiere like it’s a visit from the queen or another royal wedding.

In this soap opera, though, the real star is the story, an unpredictable roller-coaster ride, by English-period-drama standards, that would make even Susan Lucci queasy.

The second season of “Downton” is the most watched “Masterpiece” series on record, according to PBS.

Tom Holter, TPT’s programming director, said it drew an average of 120,000 viewers per episode in the Twin Cities market, a 6 percent share, or twice as many as usual for a “Masterpiece” episode.

Holter admits he didn’t watch the show himself until his college-age daughter was home for the holidays.

“We inhaled it together,” he said. “I’ve been wondering what it says about the zeitgeist, when something sweeps through like this.”

The series has also been very popular online, indicating a younger-skewing audience nationwide. Season 2 received seven times the number of video streams as Season 1, which was also more than the entire “Masterpiece” season received last year.

“None of us had any expectation of this at all,” Bonneville said. “The first time it occurred to me that we were breaking boundaries was when a lad at my son’s playground came up to me — he was about 10 or 11 — and said, ‘I don’t like that Thomas.’”

Ellen Hannaher of Minneapolis came late to the “Abbey,” but quickly became addicted, watching the first two seasons in two weekends through iTunes.

“It was like a telenovela with better acting, production, and all the drama you can handle,” she said. “I couldn’t wait to find out what happened next.”

So when a British friend downloaded it for her before it came out in the United States, “I jumped at the chance. Now my sister and I watch it together on Sunday nights and gossip about it, as we can’t tell others who have not watched it!”

Despite being better known as their characters than what’s on their driver’s licenses, the cast seems tickled pink by any recognition at all.

Joanne Froggatt, who plays elfin, unflappable Anna Bates, discovered where she stood among fans while preparing for her real-life nuptials.

“The vicar that was marrying me and my partner sent me an e-mail about details for our wedding,” said Froggatt, who has nabbed one of the show’s 27 Emmy nominations, the most ever for a non-American series. “At the bottom of the e-mail he wrote, ‘If Jo could fix it for me and my wife to go to the Downton house, she’ll go straight to heaven.’”

Coyle, whose character walks with a limp, recalls getting a letter from a fan whose physical disability had triggered a lifetime of horrible monikers. Now people call him “Mr. Bates.”

“At last, he has a cool nickname,” Coyle said.

Oscar winner Shirley MacLaine, who pops in to swap zingers with Maggie Smith’s Dowager Countess, said she was amazed to hear people gossiping about the show in countries like Thailand and Cambodia. She thinks its popularity has much to do with how creator Julian Fellowes keeps the pace at a rapid clip.

“What he’s done so brilliantly is provide 15 characters with just the right amount of time on-screen,” she said. “It really fits in with this generation’s Internet tolerance for emotional knowledge.”

Fellowes backs up MacLaine’s analysis by nicknaming his approach as “attention-deficit TV.”

When asked about inspiration, Fellowes doesn’t name-drop “Upstairs, Downstairs” or “Brideshead Revisited.” Instead he mentions “West Wing” and “ER,” two dramas jampacked with stories and characters.

“The fun is that it sort of looks like a classical period drama from the ‘70s where everyone’s bustling in and out and ringing for lunch, but the energy is much more modern,” Fellowes said. “It’s like American television series with all these plots going on, big plots, little plots, funny plots, sad plots, all plotted up together. It seems to meet what the audience wants.”

That contemporary feel is why Minneapolis’ Kris Hase is a diehard fan.

“It’s not as culturally hard to grasp as Dickens or Austen, because the family moves into modern times with a vibe that’s a lot more Hogwarts than Mansfield Park,” she said. “It’s also a fascinating study of multiple generations of diverse and strong women, so every woman has characters she can relate to.”

Fans will be happy to know that “Abbey” will return for a fourth season, although without some key players (anyone who dares to reveal the departing actors is subject to a verbal thrashing from the Dowager).

Fellowes won’t reveal how long he’ll continue the series, but did say that he’s not interested in tracking the characters, whom we first met in the wake of the 1912 Titanic sinking, past the 1920s. On the other hand, this kind of success could change anyone’s mind.

“Well, we could sort of go to the Wall Street crash,” he said. “We could end with Lord Grantham playing a ukulele.”